Electromagnetic implosion x-ray source

ABSTRACT

An electromagnetic implosion X-ray source having a thin cylindrical metal foil supported on spaced electrodes within an evacuated chamber. The electrode system is connected through a switch to a capacitor bank power supply with low inductance leads and with the average electrical impedance of the dynamic plasma being matched to the impedance of the power supply. An X-ray radiation path is provided between the X-ray source and a sample holder attached to the X-ray source.

United States Patent 1191 Baker et al.

ELECTROMAGNETIC IMPLOSION X-RAY SOURCE Inventors: William L. Baker, Columbus, Ohio; Peter John Turchi, New York, NY.

The United States of America as represented by the Secretary of the Air Force, Washington, DC

Filed: Sept. 15, 1972 Appl. No.: 289,693

Assignee:

us. (:1. 250/493, 250/522 1m. 01. H01j 35/00 Field of Search 250/493, 522

[56] References Cited OTHER PUBLICATIONS Fundamentals of Optics Jenkins et al., McGraw 11] 3,835,330 [451 Sept. 10, 1974 Hill, 1957 pp. 414 to 416.

Primary Examiner-James W. Lawrence Assistant Examiner-B. C. Anderson Attorney, Agent, or Firm-Harry A. Herbert, Jr.; Richard J. Kiiloran [57] ABSTRACT 3 Claims, 10 Drawing Figures PATENTEDSEPI 01974 SHEET 1' BF 4 I gavvvvvv- PAIENIEU SEP 1 01924 sum 2 or 4 m E In mv/ a mmmsm 01914 35,

sum u or 4 ELECTROMAGNETIC IMPLOSION X-RAY SOURCE BACKGROUND OF THE INVENTION There is a continuing effort to transform electrical energy more efficiently into an ultrashort pulse of high temperature radiation from an X-ray source. Two such prior art systems are the Z-pinch system and the adiabatic compression system.

The Z-pinch system requires a gas charge and there is a problem of energy transfer to the gas since the impedance increases too rapidly as the gas begins to accelerate, which limits the maximum current driving the plasma. The adiabatic compression schemes require extreme symmetry of the system which is difficult to maintain and also requires a gas charge.

BRIEF SUMMARY OF THE INVENTION According to this invention, a high current is driven through a very thin metallic foil cylinder in an evacuated chamber. There are three phases to the operation of the system: (1) initiation of a uniform axial current flow through the thin foil; (2) inward acceleration of the foil (now a plasma) to high kinetic energy, per particle, by the force resulting from interaction of the current with its self-magnetic azimuthal field; (3) conversion of the high kinetic energy plasma to a high temperature, high energy density plasma in the convergent geometry of an implosion. The implosion of material of high atomic number provides both high intensity bremsstrahlung, recombination and line radiation.

IN THE DRAWINGS FIG. 1 is a top plan view of an implosion X-ray source according to the invention.

FIG. 2 is a sectional view of the device of FIG. 1 along the line 22.

FIG. 3 is a sectional view of the device of FIG. 1 along the line 33.

FIG. 4 is a block diagram of an energizing system for the device of FIG. 1.

FIG. 5 shows the first step in the assembly of the foil and electrode structure for the device of FIG. 1.

FIG. 6 shows the second step in the assembly of the foil and electrode structure for the device of FIG. 1.

FIG. 7 shows how the foil is applied to the electrode structure of FIG. 1.

FIG. 8 shows how the foil is retained on the electrode structure with clamps and O-rings.

FIG. 9 is an exploded view of structure used in securing the foil to the electrode structure.

FIG. 10 shows how the lower electrode is secured to the current supply leads.

DETAILED DESCRIPTION OF THE INVENTION Reference is now made to FIGS. land 2 of the drawing which show an EM implosion X-ray source 10 having a cylindrical thin foil 12 supported on electrodes 13 and 14 held thereto by means of a pair of split clamp rings 16 and 17, which are held by means of O-rings 18 and 19. The foil should have a thickness between onehalf micron and 2 microns. The total foil height will be the active height plus about one inch for electrode attachment.

The electrode 14 is secured to a connectormember 21 by means of a plurality of screws 24, one of which is shown. The connector member 21 is connected to an annular current supply lead 28 by means of aplurality of screws 29, one of which is shown. An indium ring 31 is located between connector member 21 and lead 28 to provide good contact and to reduce the inductance in the current supply path. A backing plate 33 for electrode 14 is secured to connector member 21 by means of a plurality of screws 35, one of which is shown.

The other electrode 13 is connected to annular current supply lead 36 by means of annular connectors 38 and 39 and the clamp ring 16. The connector 39 is connected to the lead 36 by means of screws 41, one of which is shown. The connector 38 is secured to connector 39 by means of screws 43 which also pass through an annular stainless steel electrode support 45 and an annular stainless steel spacer 47. Electrode 13 is secured to support 45 by means of a plurality of screws 49, one of which is shown. A top hexagonal plate member 53 and hexagonal member 55, with circular central chamber, are secured to lead member 36 by means of screws 57 to provide a closed chamber. A viewing window 58 of a material such as glass or a clear plastic may be secured to the plate member 53 by means of a stainless steel retaining ring 59 and a plurality of screws 61, one of which is shown; A bottom plate member 63 is secured to lead 28 by means of screws 64, one of which is shown. O-rings 65, 66, 67, 68, 69 and 70 provide seals for the chamber to permit evacuation by means of a vacuum pump 72 secured to port 74 through a conduit 75. A plurality of holes 76 are provided in spacer member 47 to permit evacuation of the system. Holes 78 used as a passage for a wrench to tighten socket head screws 23 and additional holes 79 provide for evacuation in the space between the electrodes l3 and 14.

The leads 28 and 36 are insulated by means of insulator 81 which may be a Mylar sheet sandwiched between two polyethylene sheets. A polyethylene insulator 83 is provided between connector member 21 and connector member 39 and extends between leads 28 and 36 to overlap insulator 81. The edge of insulator 83 stops at or below the top of electrode 14 to keep the in- .sulator out of the path of radiation from foil 12.

A sample holder 85 is positioned adjacent bottom plate member 63. A stainless steel tubular member 87, welded to a stainless steel flange member 88, is also sealed to sample holder 85, by means not shown, so that the sample holder is evacuated with the rest of the system through aperture in electrode 14, aperture 91 in backing electrode 33 and aperture 93 in plate member 63. Apertures 90, 91 and 93 also provide a radiation path to the sample in the sample holder 85. A conventional Rogowski coil 94 may be provided for current monitoring.

The X-ray source 10 is energized from a capacitor bank power supply 95 through a switching device 96,

as shown in FIG. 4.

While more than one of some of the screws would normally show in the drawing, only one of each is shown in their relative positions to simplify the drawing. For example, since the cut on the left side of FIG.

2 is displaced 15 from the showing on the right side, as can be seen from FIG. 1, the screws shown on the left side will all be spaced 15 from those shown on the right side. Therefore, only one of each is shown. All material not otherwise specified is aluminum.

In assembling the device, insulators 81 and 83 are positioned between leads 28 and 39 and connector 21,

with backing plate 33 attached, is secured to electrode 28 with the indium ring 31 filling the voids to provide good contact. Connector 39 is then secured to lead 36 with insulator 83 being positioned between connectors 21 and 39.

The thin foil 12 is secured to electrodes 13 and 14 in the manner shown in FIGS. 5-10. Socket head screws 23 are first inserted in the holes in bottom electrode 14. Then three spacer blocks 101 are positioned between electrodes 13 and 14, as shown in FIG. 5. The electrodes are then clamped together with a plurality of clamps 103, two of which are shown. Three holes 104, 120 apart are then drilled through electrode 13 extending part way through electrode 14. The holes are then tapped, as shown in FIG. 5. Threaded rods 105 are then inserted in the tapped holes, as shown in FIG. 6.

The spacers 101 are then removed and a thin foil ribbon 12 is applied, as shown in FIG. 7. The electrode rims 13 and 14' are wetted with a liquid, such as water, to aid in holding the foil to the electrode. The amount of wetting should be just enough to permit adjustment and smoothing of the foil. The water is readily removed in the evacuation process. The foil is cut to fit around the electrodes with no overlap.

The clamp rings 16 and 17 are then placed over the foil, as shown in FIGS. 8, 9 and 10. Each clamp ring is made up of three segments separated by spacers 15. After the O-rings 18 and 19 are in place, the spacers are removed to permit the clamp rings to evenly clamp the foil to the electrodes.

The electrode assembly is then secured to connector member 21 by aligning the socket head screws 23 with holes in the connector member 21 and by tightening the screws with an Allen wrench, 106, passed through holes 78 in the electrode 13. Clamp ring 17 is then secured to connector member 21 with screws 24. Connector 38, support 45 and spacer 47 are then secured to connector 39 with screws 43. Electrode 13 is then secured to support 45 with screws 49. Rods 105 are then removed and plate member 53 and annular member 55 are secured to lead 36. Bottom plate member-63 with sample holder 85 attached is then secured to lead 28.

Evacuation pump 72 is then secured to port 74 and the power supply is connected to leads 28 and 36. The exact connection made to leads 28 and 36 depends upon the particular power supply used.

In one design of the apparatus, the capacitor bank power supply has the following characteristics.

Charging Voltage 50 kilovolts Capacitance 400 microfarads Stored Energy 500 kilojoules Peak Current to Matched Load megamperas Rise-Time 600 nanoseconds Pulse Length 1.2 microseconds The dimensions of the implosion X-ray system used with this power supply are as follows:

Initial Foil Radius 8 cm Continued Active Foil Height l cm Foil Thickness 1 micron Foil Material Aluminum The implosion characteristics for such a system are as follows:

Implosion Speed 2 X 10 cmlscc Kinetic Energy Per Particle 5.4 Kev Total Plasma Kinetic Energy 300 kilojoules Transfer Efficiency (Total Kinetic Energy/Initial Bank Energy) 60% in the operation of the device, the discharge chamber is evacuated to 10 torr.

Upon closing the switch 96, a uniform axial current flows through the foil cylinder which converts the foil to a plasma which accelerates inwardly to high kinetic energy per particle by the interaction of the current with its self magnetic field.

-.The X-rays produced by the implosion pass out through apertures 90, 91 and 93 to irradiate the sample in sample holder 85.

Other arrangements for making use of the X-rays than that shown may be provided.

There is thus provided a system for creating a more powerful X-ray source by more efficiently transforming electrical energy into an ultrashort pulse, approximately 10 sec or less, of high temperature radiation of ev or higher.

We claim:

1. An implosion X-ray apparatus, comprising: an enclosed container; means for evacuating said container to a predetermined vacuum; a first disc-shaped electrode within said container; at second disc-shaped electrode within said chamber spaced a predetermined distance from said first electrode; a thin cylindrical electrically conducting foil secured to the outer cylindrical surfaces of said electrodes; means for supplying a high energy current pulse to said electrodes and foil to thereby convert said foil to a high temperature, high energy density plasma and means for providn g an X-ray path from the space between said electrodes external to said container whereby said X-rays produced by implosion of said plasma may be utilized.

2. The device as recited in claim 1 including a three part split clamp ring surrounding said foil adjacent the outer cylindrical surface of each electrode and an O- ring retaining the split clamp rings in position around the foil and the electrodes.

3. The device as recited in claim 2 including means for viewing the implosion between the electrodes. 

1. An implosion X-ray apparatus, comprising: an enclosed container; means for evacuating said container to a predetermined vacuum; a first disc-shaped electrode witHin said container; a second disc-shaped electrode within said chamber spaced a predetermined distance from said first electrode; a thin cylindrical electrically conducting foil secured to the outer cylindrical surfaces of said electrodes; means for supplying a high energy current pulse to said electrodes and foil to thereby convert said foil to a high temperature, high energy density plasma and means for providng an X-ray path from the space between said electrodes external to said container whereby said X-rays produced by implosion of said plasma may be utilized.
 2. The device as recited in claim 1 including a three part split clamp ring surrounding said foil adjacent the outer cylindrical surface of each electrode and an O-ring retaining the split clamp rings in position around the foil and the electrodes.
 3. The device as recited in claim 2 including means for viewing the implosion between the electrodes. 